In the first stage of brewing a mash is prepared by adding water to ground malt which, in many cases, also contains a cooked carbohydrate adjunct such as corn grits or rice. The temperature is raised to favor the enzymatic hydrolysis of the carbohydrates in the mash. When hydrolysis is complete the liquid (wort) is filtered through the solid residue. The wort continues through the brewing process and eventually becomes beer. The solid residue which remains after filtration of the wort is called brewer's spent grain (BSG) and is a by-product of the brewing industry. Twelve and a half pounds (dry basis) of BSG are produced for every barrel of beer, amounting to over 700,000 tons dry weight annually in the United States. The large amount of BSG produced has, at times, been a disposal problem. The most common use of BSG has been as a feed for ruminants.
The spent grain consists mainly of the pericarp and hull portions of the barley and of nonstarchy parts of corn if corn grits are used as an adjunct. Although "spent" in terms of carbohydrate, BSG is higher in protein, lipids, and fiber than was the original barley-adjunct mixture.
Efforts to convert the BSG into an additive for food products for human consumption have been handicapped by the presence in the BSG of barley hulls. The barley hulls have a rough texture and when ground tend to break into long sharp slivers which are unpalatable and difficult to remove.
There are three objectives which could be fulfilled by putting BSG in human food:
1. The protein and fiber contents of the food containing the BSG would be increased. PA1 2. By direct human consumption, better utilization of the food resource would be made. PA1 3. The brewers who produce the BSG would be paid a higher price for their product.
In order for those three objectives to be fulfilled, appreciable quantities of food containing BSG would have to be consumed.
There is evidence that indicates that lack of dietary fiber in the human diet may contribute to the occurrence of certain noninfectious diseases such as diverticulosis, colon cancer, hemorrhoids, arteriosclerosis, varicose veins and appendicitis.
Dietary fiber is normally defined as the skeletal components of the plant cell which are resistant to digestion by enzymes in the human digestive tract. Dietary fiber includes hemicelluloses, pectin substances, gums and other carbohydrates as well as lignin and cellulose. BSG, because it is high in both fiber and protein, is a good candidate to be added to human food as a protein and fiber supplement.
Dietary fiber is in demand because of the benefits which are said to accompany its consumption. The physiological claims for dietary fiber include its use for relieving constipation by increasing the water content of the feces, for treating or preventing diverticular disease and for possibly reducing serum cholesterol. Therefore, there is an interest in supplementing processed food products for human consumption with dietary fiber. Most of the dietary fiber which is added to such food products today comes from white wheat bran. Other sources include oats, corn bran, soy bran, rice bran and finely divided cellulose, including wood cellulose.
In the past, various efforts have been made to incorporate BSG into bread and bakery products.
Finley and Hanamoto (Cereal Chem. 57:166, 1980) milled BSG on a Quadramat Sr. flour mill into two bran fractions, a shorts fraction, and a flour fraction. Each fraction was added to a bread formula at 6 and 12% flour replacement levels. Loaf weights and volumes were measured and loaf quality characteristics were judged. The two bran fractions depressed loaf volume less and were less detrimental to bread quality than the flour or shorts fractions, but at the 12% replacement level all bread was judged unsatisfactory. No attempt was made to alter the fractionation made by the milling system and no special treatments were used to improve the quality of the bread containing the BSG.
In another bread study, Prentice and D'Appolonie (Cereal Chem. 54:1084, 1977) used BSG in bread at 5, 10, and 15% flour replacement levels. The bread was evaluated by a taste panel and compared to a control that contained 30% whole wheat flour and 70% wheat flour. There was no significant preference shown between the control and bread containing 5 and 10% BSG. The 30% whole wheat control was significantly preferred over the bread having 15% BSG.
Prentice et al. (Cereal Chem. 55:712, 1978) replaced soft wheat flour with ground BSG in cookie formulas. They found that the addition of soy lecithin to a cookie dough containing BSG improved cookie quality.
A survey conducted by the USDA to determine consumer awareness and attitudes on food grading showed that consumers are more concerned about the quality of bread than nutrition or any other characteristic. Quality was important to 61%, type of bread to 35.9%, brand to 33.8%, price to 30.9%, ingredients to 16.3%, and nutrition to only 8.7%. Therefore, the nutritional value alone will not be sufficient to sell BSG. If the three objectives listed above are to be met by putting BSG in bread, a high quality bread containing BSG must be made.